Telephone line circuit



Aug. 4, 1942. G. R. EATON TELEPHONE LINE CIRCUIT Filed April '7, 1941 M 511111111! QLB 4h n u x u w u c h M n L z. w m F .u .2 .iLr. rlill lllllr lllllllllllllllll ||l w m M m I 9 6 8 W m c L I n .ID I n m 4 5 2 7) L 3 6 LP A m w I M S A 2 w m W7 Patented Aug. 4, 1942 UNITED STATES PATENT OFFICE TELEPHONE LINE CIRCUIT Application April 7, 1941, Serial No. 387,151

8 Claims.

This invention relates to telephone line circuits and its object is the provision of a new and improved line circuit in which the number of relays is reduced to a minimum without a corresponding reduction in the number of functions performed thereby.

A specific object of the invention is the provision of an improved, two-relay line circuit wherein the relay perform the usual line-relay and cutoff-relay functions, and also serve to take over the function of a lookout relay to lock the asso- 'ciated line out of normal service, when the line is out of order, or when a revertive call has been made thereon.

A feature of the invention is that the line relay is restored in the usual manner when the associated cutoff relay operates upon an extension of the calling line, as by a finder, but may be reoperated, with the cutoff relay operated, and the concurrent operation of the two relays causes the line to be locked out of normal service until the line is cleared.

A specific feature of the invention is that the cutoff relay of the line circuit is a twostep relay and is arranged to operate through its first step only in the performance of its cutoff-relay function, and operates through its second step only in the event that the line circuit is to be placed in its lockout condition, to lock the associated line out of normal service by the concurrent action of both relays.

The foregoing and other objects and features of the invention will become more apparent as the description progresses.

Referring now to the accompanying drawing,

comprising Figures 1 and 2, they show a sumcient amount of the equipment used in a telephone system embodying the features of the invention to enable the invention to be understood.

Figure 1 illustrates a line circuit LC, constructed in accordance with the features of the invention, in association with an automatic telephone line L having one or more substations A thereon, and common switching equipment indicated at CSE.

Figure 2 illustrates a preferred embodiment of the two-step cutoff relay C of Figure 1.

Referring now particularly to Figure l, the illustrated line circuit LC is individual to the line L, having substation A thereon, and, if a party line, having one or more other substations bridged across the conductors 2 and 3 thereof. The line circuit LC includes th marginal, twostep cutoff relay CO, and has associated there with, the usual so-called tip, ring, and sleeve conductors T, R, and S, respectively.

The conductors T, R, and S may be extended by common switching equipment indicated at CSE to other lines similar to th line L, as calls are made from the line L; and the common switching equipment CSE may operate to extend connections to the line L and the line circuit LC over the conductors T, R, and S.

The line circuit LC is provided with an individual marking conductor l0, over which the line L is marked as calling, when a call is initiated thereon, together with the start conductor ll, common to a group of lines, to start an idle finder in the equipment CSE to search for the calling line.

It is to be observed that cutoff relay CO is provided with armature contact-springs 4, 5, 6, and 1. It is to be observed that armature contactsprings 4, 5, and l (termed armatures for convenience) are each provided with a back contact, as well as with a front contact, while armature 6 is provided with only a front contact. The arrangement of these springs may be varied as desired, dependin upon the particular circuit arrangement to be used in carrying out the invention. It is to be observed that each of the back contacts associated with armatures 4 and 1 has the Roman numeral I associated therewith, indicating that the contact is broken upon the firststep movement of the two-step relay. It is to be observed further that each of the other contacts of the relay CO has the Roman numeral II associated therewith indicative of the fact that these other contacts are affected only when the relay CO is actuated through its second step.

Referring now to Figure 2, the cutoff relay C0 of Figure 1 is shown therein as having the usual spool type of winding surrounding the usual type of core, the winding bein provided with terminals 2| and 23. The winding is held in assembled relationship to the so-called heel piece 24 by a nut threaded onto the screw portion 22.

Relay CO is provided with a generally L- shaped armature 25 pivoted 0n the exposed end of heel piece 24. The armature 25 is normally maintained in its illustrated, restored position by the tension of the associated contact springs, such as the springs at spring group 30. When the winding of the relay is energized by the passage of current therethrough, by way of terminals 2i and 23, the attraction between the exposed end portion 26 of the winding core and the associated end of armature 25 results in the rotation of the armature in a clockwise direction to actuate the associated contact springs.

Stop spring 28 is attached to armature 25, as by screw 21, and is adjusted so as to come into contact with spool head 29 when the armature has moved only part way toward the exposed core portion 25. The spring 23 has sufficient stiffness to definitely arrest the armature movement in its first-step, partially operated position when the winding of the relay is only normally energized.

When the winding of relay CO is excessively energized, under conditions to be pointed out hereinafter, the attractive force is sufficient to overcome the stiffness of spring 28 and thereby draw the end of armature into contact with the exposed end of winding core 26. This additional movement is termed the second step of the cutoff relay and is effective to complete the movement of the associated contact springs.

Of the contact springs including armature springs 4 to 1 illustrated in Figure 1, only the armature springs B and 1 and the contact springs associated therewith, are illustrated in the spring assembly in Figure 2. It is understood, of course, that relays are customarily provided with separate spring assemblies laid side by side on the heel piece so as to be operated by the armature of the relay. It will be understood, therefore, that an additional contact-spring assembly similar to 38, containing armatures 4 and 5 of Figure l and their associated contacts, is located directly behind the contact-spring assembly 38 and similarly operated by armature 25.

A detailed description of the operation of the improved line circuit follows.

An incoming call When the line L is called, and the associated conductors T, R, and S are seized by the common switching equipment CSE, a battery potential, through a resistor such as I5, may be applied to conductor S and its multiples to guard the called line against intrusion. The placing of this po- 5 and 6 remain uneffected, for the relay does not operate through its second step.

Asa result of the above-described first-step operation of relay CO, the called line is cleared for ringing and talking purposes.

When the connection made to the line is sub- I sequently broken by the common switching equipment CSE, the line is freed and relay CO restores.

An outgoing call When an outgoing call is to be made from the line L, such as from substation A, the removal of the receiver at the calling substation results in the closing of a loop or bridge across the conductors 2 and 3 of the line L. By this operation, a circuit is closed, from the ground connection normally made to conductor 2 at armature ll and its arresting contact, over the calling line, for the winding of relay LR, normally connected to conductor 2 through armature l and its arresting contact. Line relay LR prepares a now-ineffective locking circuit for relay CO at armature 9, while at armature 8 it disconnects ground potential from individual marking conductor It to mark the line L as calling, at the same time extending ground potential to the common, or

group, start conductor H to start finder equipment in the common switching equipment CSE in search of the calling line.

When the calling line is reached, the absence of ground potential on marking conductor l0 causes the line to be seized over conductors T, R, and S. At this time, battery potential, as by way of resistor l5 in equipment CSE, is applied to sleeve lead S, closing a circuit for the winding of cutoff relay CO. As before described, relay C0 operates through its first step only at this time because it receives only a normal amount of energizing current through a resistor such as [5. Relay CO, therefore, operates only armatures 4 and 1, and these armatures move only sumciently to disconnect from their associated back contacts. As a result, line conductors 3 and 2 are cleared in the line circuit LC.

Line relay LR now restores to unground start conductor H, at armature 8, at the same time re-grounding marking conductor iii to terminate the calling marking thereof.

In the common switching equipment CSE, the new extended conductors T and R are connected with a link having a line relay and a balancing retard coil connected thereto, such as relay l3 and retard coil H5. Relay I3 is now connected between ground and the tip conductor T, while retard coil M is connected between the free pole of the exchange battery and ring conductor R. Current now flows through relay 22, from battery supplied through retard coil 14, and over the calling line. Relay 13 now operates over the calling line to prepare for the directive extension of the calling line responsive to the dialing of the desired number.

The subscriber at the calling substation, such as substation A, may now cause the common switching equipment CSE to respond to controlled restorations of relay G3 to extend the connection toward the desired line, by operating the usual type of calling device, including the interrupter springs illustrated at substation A.

The connection may be made with the called line, or refused, according to whether or not the line isbusy.

When the connection is to be released, the subscriber at the calling substation replaces his receiver, thereby opening the bridge or loop across conductors 2 and 3 responsive to which relay l3 in the common switching equipment CSE releases and causes the connection to be released in the usual manner, whereupon battery potential is disconnected frorn sleeve lead S. When this occurs, relay CO restores, thereby returning the line circuit to its illustrated normal position.

Trouble operation Let it be assumed that the conductors 2 and 3 of the line LR are looped or bridged accidentally, such as by a shorted or grounded line condition, or by an unnoticed accidental removal of the receiver at a substation thereon. When this occurs, line relay LR operates as before explained, with the result that an idle finder in the common equipment CSE searches for and connects with the line L by way of leads T, R, and S. Cutofi relay CO is thereupon operated through its first step over the sleeve lead S, as by way of resistor [3, to clear the line L of line relay LR and ground.

Since the extension of the line L and line circuit LC, by way of the common equipment CSE under the assumed condition is an accidental one, no dialing occurs, and a portion of the common switching equipment CSE is thus needlessly held by the trouble condition on the line L. In order to clear the held portion of the common switching equipment and return it to common use, and to prevent the line L from again causing the seizure of any portion of the common equipment until the trouble has been cleared, means including the timing contacts TC is provided for bringing the line circuit LC into its lockout condition.

It should be recalled that the seized link in the common equipment is prepared for operation, and is held seized, under the control of the relay therein such as relay l3.

When no dialing has occurred for a predetermined interval after the seizure of the common switching equipment CSE, the failure of relay 13 to respond to circuit interruptions at the calling device permits timing contacts TC to close a circuit for a clear-out relay, such as l2. When relay I2 operates, it applies battery potential more directly to the sleeve S, through a circuit path which does not include a resistor such as I5, thereby providing a sufficiently increased current flow through the winding of cutoif relay CO to permit this relay to operate fully.

Upon operating fully, cutoff relay CO reconmeets the disconnected line relay LR and ground potential to line conductors 2 and 3 at the front contacts of armatures I and 4, respectively, while at armature 6, relay CO prepares a local locking circuit for itself.

Line relay LR now operates over the line L, because of the looped, bridged, or shorted condition of the conductors 2 and 3. At armature 9, relay LR completes a locking circuit through the resistor I6, and through actuated armature 6 and its front contact, for relay CO, to hold relay CO fully operated as long as the trouble condition remains on the conductors on the line L.

Relay CO is able to remain fully operated when supplied with less current than was required to operate it through its second step as is well known. Relay therefore remains operated in series with the resistor switching equipment CSE has cleared out, and no battery potential is applied to conductor S except by way of resistor l6 and the actuated armatures 9 and 6. This battery potential now serves to mark the line LC as busy to prevent seizure of the line L as a called line.

Line relay LR also actuates its armature 8, as it does when the line relay is being operated to indicate a calling condition on the associated line. is of no effect for armature 5 of relay CO is operated.

When the trouble condition (a looped, bridged, or shorted condition of conductors 2 and 3 of the line L) is cleared, line relay LR restores and opens the locking circuit of cutoff relay CO at armature 9, whereupon relay CO restores to place the line circuit LC in normal condition.

Although a preferred embodiment of the in vention has been shown, specially adapted to operate with a particular switching system, it is to be understood that the invention may be employed with other switching systems without departing from the invention as defined by the appended claims.

What is claimed is:

1. In a telephone system wherein automatic switching equipment is provided in common for interconnecting telephone lines, a line circuit for the individual use of one of said telephone lines,

l6 after the common 1 At this time, the operation of armature 8 1 said line circuit including a line relay operable over the associated line to indicate the origination of a call thereon, a cutoff relay associated with said line relay and operable to disconnect the line relay from the line to clear the line for talking purposes, said cutoff relay being capable of both a partial operation and a full operation, means effective during the normal operation of the line and associated line circuit in cooperation with the common switching equipment for insuring that the cutoff relay is only partially operated, means operable from the common switching equipment in the event that the line associated With said line circuit is out of order for operating said cutoff relay fully, said cutoff relay serving when operated fully to reconnect said line relay to the line to permit the line relay to reoperate thereover, and contacts associated with said relays effective when the cutoff relay is operated fully and the line relay is reoperated to maintain both relays operated under the control of the associated line to thereby lock the line out of normal service.

2. In a telephone system wherein automatic switching equipment is provided in common for interconnecting telephone lines, a line circuit for the individual use of one of said telephone lines, said line circuit including a line relay operable over the associated line to indicate the origination of a call thereon, a cutoff relay associated with said line relay and operable to disconnect the line relay from the line to clear the line for talking purposes, said cutoff relay being capable of both a partial operation and a full operation, means effective during the normal operation of the line and associated line circuit in cooperation with the common switching equipment for insuring that the cutoff relay is only partially operated, means effective when there exists a shorted or similar abnormal condition of the line for operating the cutoff relay fully, said cutoff relay serving, when operated fully, to reconnect the line relay to the line to permit it to reoperate thereover, said relays cooperating when both are fully operated at the same time to lock the line out of normal service.

3. In a telephone system, a line relay individual to a subscriber line, and means for operating said line relay over said line responsive to the removal of a receiver thereon to indicate a calling condition on the line, switching means effective to extend a connection from said calling line, a marginal two-step cutoff relay and means for operating it through its first step over the extended connection to disconnect said line relay, means operable over the extended connection for increasing the current flow through said cutoff relay when there is a special condition on said line to operate said relay through its second step, said cutoff relay being effective to reconnect the line relay when operated through its second step, circuit connections controlled by said relays for jointly maintaining both relays operated under the control of the line so long as the said special condition remains thereon.

4, In a line circuit for use in association with a line individual thereto, a line relay operable over said line, a cutoff relay partially operable to disconnect the line relay, said cutoff relay being effective to reconnect the line relay when operated fully, means effective under predetermined conditions for operating the cutoff relay only partially and for maintaining it only partially operated thereafter, and means effective under other predetermined conditions for oper- 'ating the cutofi relay fully to reconnect the line relay to the line.

5. In a line circuit for use in association with a line individual thereto, a line relay operable over the associated line, a cutoff relay partially operable to disconnect the line relay, said cutoff relay being efiective to reconnect the line relay when operated fully, means effective under predetermined conditions for operating the cutoff relay only partially and for maintaining it only partially operated thereafter, and means effective under other predetermined conditions for operating the cutoff relay fully to reconnect the line relay to the line, and a local locking circuit for said cutoff relay controlled by the line relay and effective only when the ine relay is operated and the cutoff relay is fully operated.

6. In a telephone system, a line circuit including a line relay and a cutoff relay, said relays being operable separately to perform their respective line-relay and cutoff-relay functions, said cutoff relay having a first-step position into which it is operated to perform its cutoif function and a second-step position into which it is not normally operated, and means for operating said cutoif relay to said second-step position and for concurrently operating the line relay to lock the associated line out of service.

7. In a telephone system, a line circuit including a line relay and cutoff relay separately operable to perform their respective separate functions, one function of the cutoff relay being to disconnect the line relay from the associated line when the cutoff relay is only partially energized, means including contact means controlled by further movement of said armature in the same direction for reconnecting said line relay when the cutoff relay is fully energized, means normally operating to secure only the partial energization of said cutoff relay to secure only the performance of the normal cutoff-relay functions, and means effective under predetermined conditions for bringing about a full energization of the cutoff relay to cause it to operate fully to reconnect said line relay.

8. A line circuit for use in a telephone system comprising a line relay arranged to initiate automatic line-finder action to secure extension of a calling line, a combined two-step cutoff and lockout relay arranged on its first step to release the line relay after the calling line has been extended, means arranged to effect a secondstep operation of the said cutoff relay when a condition of trouble exists on the line whereby said cutoff relay effects the energization of the line relay over the line circuit, and means controlled in turn by said line relay to hold said two-step cutofi relay in its second-step position, during the continuance of said trouble condition.

GEORGE R. EATON. 

